On the uplink in W-CDMA, user-specific scrambling codes are applied by way of multiplication to user apparatuses (UE: User Equipment) in the same cell to allow non-orthogonal reception, and therefore fast transmission power control (TPC) for reducing the influence of multi-user interference (that is to say, near-far problem) is essential.
In the LTE (Long Term Evolution) system defined in 3GPP Release 8 (hereinafter abbreviated as “Rel-8 LTE”), SC-FDMA (Single-Carrier Frequency Division Multiple Access) radio access, which realizes a low peak-to-average power ratio (PAPR) and which is effective to expand the coverage, is employed on the uplink. Consequently, by means of scheduling by a radio base station apparatus, a radio resource having a certain frequency and time is allocated to one UE, and therefore orthogonality is achieved between users in the same cell in the frequency and time domains. Consequently, fast TPC is not necessarily essential from the perspective of reducing multi-user interference in the same cell. However, since Rel-8 LTE is based on one-cell frequency repetition, there is significant interference from the surrounding cells, and, in particular, the interference level from UEs located at cell edges is high. Consequently, to compensate for such surrounding-cell interference and maintain certain reception quality, TPC has to be adopted in LTE as well.
The transmission power of signals transmitted on the uplink of the LTE system (including the PUSCH (Physical Uplink Shared Channel), PUCCH (Physical Uplink Control Channel) and SRS (Sounding Reference Signal)) is controlled by the combination of open-loop control, which is based on parameters (Po, α, and so on) reported from the radio base station apparatus in a comparatively long cycle and propagation loss (path loss (PL)) measured by the mobile terminal apparatus, and closed-loop control, which is based on TPC commands reported from the radio base station apparatus in a comparatively short cycle based on the situation of communication between the radio base station apparatus and the mobile terminal apparatus (reception SINR (Signal to Interference plus Noise Power Ratio)) (see, for example, non-patent literature 1).